Comparative study of the effect of Mg, Zn and Ag dopants on properties of titanium dioxide as mesoporous ETL for photovoltaic application

Abstract

As the electron transport layer (ETL) has a pivotal role in extracting and transporting the photogenerated electrons leading to lesser recombination of charge carriers in perovskite solar cells (PSCs), we reported on the modification of structural, optoelectronic and optical characteristics of ETL of PSCs. ETL (titanium dioxide, (TiO2)) modified by incorporation of metal ion dopants magnesium, zinc, and silver named Mg–TiO2, Zn–TiO2, Ag–TiO2 respectively revealed fascinating characteristics in terms of electron injection, porosity, diffusion length, and nonlinear optical properties. The decrease in bandgap Ag–TiO2 < Zn–TiO2 < Mg–TiO2 < TiO2 aligned the TiO2 conduction and valence band which makes the injection of electrons from perovskite active layer conduction band to ETL conduction band easier. This helped to get reduced recombination and enhanced electron transport. Surface morphology revealed the increase in porosity as Ag–TiO2 > Zn–TiO2 > Mg–TiO2 > TiO2 which suggested the easy infiltration of the perovskite active layer into ETL and lead to enhanced absorption of the incident light. Optoelectronic characterization by steady-state photocarrier grating technique gave an increase in minority charge carriers diffusion length Ag–TiO2 (99 nm) > Zn–TiO2 (70 nm) > Mg–TiO2 (67 nm) > TiO2 (61 nm). Nonlinear susceptibility of third-order (χ (3)) obtained by the z-scan technique is of the same order for TiO2, Mg–TiO2, Zn–TiO2 whereas it decreases for Ag–TiO2. With the help of obtained experimental results, the authors concluded that Ag–TiO2 is the promising ETL among the introduced materials followed by Zn–TiO2, Mg–TiO2, and TiO2.